title: Identification of nodal tissue in the living heart using rapid scanning fiber-optics confocal microscopy and extracellular fluorophores.
abstract: BACKGROUND
  Risks associated with pediatric reconstructive heart surgery include injury of the sinoatrial node (SAN) and atrioventricular node (AVN), requiring cardiac rhythm management using implantable pacemakers. These injuries are the result of difficulties in identifying nodal tissues intraoperatively. Here we describe an approach based on confocal microscopy and extracellular fluorophores to quantify tissue microstructure and identify nodal tissue.
  
  
  RESULTS
  Using conventional 3-dimensional confocal microscopy we investigated the microstructural arrangement of SAN, AVN, and atrial working myocardium (AWM) in fixed rat heart. AWM exhibited a regular striated arrangement of the extracellular space. In contrast, SAN and AVN had an irregular, reticulated arrangement. AWM, SAN, and AVN tissues were beneath a thin surface layer of tissue that did not obstruct confocal microscopic imaging. Subsequently, we imaged tissues in living rat hearts with real-time fiber-optics confocal microscopy. Fiber-optics confocal microscopy images resembled images acquired with conventional confocal microscopy. We investigated spatial regularity of tissue microstructure from Fourier analysis and second-order image moments. Fourier analysis of fiber-optics confocal microscopy images showed that the spatial regularity of AWM was greater than that of nodal tissues (37.5 ± 5.0% versus 24.3 ± 3.9% for SAN and 23.8 ± 3.7% for AVN; P<0.05). Similar differences of spatial regularities were revealed from second-order image moments (50.0 ± 7.3% for AWM versus 29.3 ± 6.7% for SAN and 27.3 ± 5.5% for AVN; P<0.05).
  
  
  CONCLUSIONS
  The study demonstrates feasibility of identifying nodal tissue in living heart using extracellular fluorophores and fiber-optics confocal microscopy. Application of the approach in pediatric reconstructive heart surgery may reduce risks of injuring nodal tissues.
authors.affiliation: Department of Bioengineering and Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, Utah; and Division of Pediatric Cardiothoracic Surgery, Department of Surgery, University of Utah School of Medicine, Salt Lake City, Utah.
authors.forename: Chao
authors.initials: C
authors.lastname: Huang
authors.forename: Aditya K
authors.initials: AK
authors.lastname: Kaza
authors.forename: Robert W
authors.initials: RW
authors.lastname: Hitchcock
authors.forename: Frank B
authors.initials: FB
authors.lastname: Sachse
mesh_terms: D000818:Animals; D001283:Atrioventricular Node / Q000033:anatomy & histology*; D003199:Computer Systems; D005240:Feasibility Studies; D005336:Fiber Optic Technology; D019084:Fluorescent Antibody Technique, Indirect; D005456:Fluorescent Dyes; D005583:Fourier Analysis; D007091:Image Processing, Computer-Assisted; D008297:Male; D018613:Microscopy, Confocal; D015233:Models, Statistical; D057054:Molecular Imaging / Q000379:methods*; D010210:Papillary Muscles / Q000033:anatomy & histology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012849:Sinoatrial Node / Q000033:anatomy & histology*
chemical_list: D005456:Fluorescent Dyes
keywords: 2-dimensional; atrioventricular node; confocal imaging; congenital cardiac defect; sinoatrial node